I have shell scripts like

while true;do
   #Code HERE!
   #Pushing Data to DB
   echo "Data to DB"> /root/schip.log 2>&1

This is script is continuously running and gathering info on server and then sending data to DB(TimeStamp DB). I don't why, sometimes the scripts are dieing. In logs I can't see any thing. In same way, I saw in Python script. Python script like this

import <stuff>
while True:
   #Code HERE
   #Push data to DB
   print "Data to DB"

So, what could be the reasons?, how do I prevent? and how can I enable the logs(In python and Shell) to know the reason?. Thanks!

  • do any of the scripts have set -e in them? if so, then any error or any non-zero exit code from any command (e.g. while shoveling data into the db) would cause the script to exit. – cas Oct 27 '15 at 7:27
  • No, there no set -e in scripts. In Python script, I'm using potsdb module to push data to Time stamp DB like this metrics = potsdb.Client(<serverIP><serverPort>) then metrics.send(<metrics_name>, <Tag1=value1>). So, there could be problem while pushing to DB? – Veerendra Kakumanu Oct 27 '15 at 7:33
  • So, what was it in the end? – Stéphane Chazelas Oct 27 '15 at 12:53

A few things that may cause a shell to exit (not exhaustive):

  • calling the exit utility. Let's not forget about the obvious
  • calling the return utility. In the case of bash that will return only if in a function or sourced file.
  • exec cmd. That will execute cmd in the same process so in effect breaking out of that loop. The script will end when cmd exits.
  • set -e/set -o errexit is enabled (see also the SHELLOPTS environment variable for bash) and a command exits with an error.
  • set -u/set -o nounset is enabled and an unset variable is referenced.
  • a DEBUG or ERR trap is defined that calls exit.
  • Failing special builtins. Failure of special builtins (like set, :, eval...) causes the shell to exit. In the case of bash though, that only happens in POSIX mode (like when POSIXLY_CORRECT is in the environment or when invoked as sh...) and even then not for all special builtins. For instance : > / will cause the shell to exit.
  • as mentioned by @schily, syntax error (like in code that is only reached conditionally).
  • division by 0 (in $((1/x)) or ${array[1/x]}).
  • internal bash error for instance because some limit is reached:
    • fails to allocate memory
    • fails to fork a process
    • stack size exceeded (for instance when using function recursion)
    • Some other limits in place via ulimit (which may also cause some signals to be sent).
  • killed by a another process. Another process can call kill() to explicitly kill the interpreter of your script.
  • killed by the system.
    • SIGINT/SIGQUIT. If you press ^C/^\.
    • SIGHUP. If the terminal is disconnected.
    • SIGSEGV/SIGBUS/SIGILL. The bash command does something wrong (a bug) or failing hardware (memory).
    • SIGPIPE: builtin (echo, printf) writing to a now-closed pipe or socket (could also happen for error messages if stderr is a pipe).

The first thing to check would be the error messages and the exit status.

| improve this answer | |

A syntax error in a script will terminate the script.

If your script code includes shell variables that may include spaces in some cases, this may cause a syntax error in case the shell variable is not enclosed in double quotes.

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  • Script is not terminating because of syntax error, I checked. I removed while statements and then I executed->Works Fine!. Actually, I ran those script with nohup like nohup sh script.sh &, that will create the nohup.out. I can tail -f nohup.out to view the data weather, it is running or not->This is also works fine(But suddenly it dieing! somtime) – Veerendra Kakumanu Oct 27 '15 at 12:47
  • 1
    You are mistaken: even with bash, scripts terminate from a syntax error. You may try to set -x to get the location in the script that aborts. – schily Oct 27 '15 at 12:55

Possibly your Shell is sourcing some external code with the "." command.
That code is interpreted by the same shell instance. If that code has a syntax error or that code performs an "exit", the calling script halts. It is possible that this script is not called at each loop so your job is running a while before it fails.

example with a syntax error that will fails after 3 loops

while true
let i=i-1
[ $i -eq 0 ] && . ./a 2>/dev/null

sleep 2

"a" script is missing "fi"

if  true
   echo a 
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